This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Posttranslational modifications (PTMs) play essential roles in protein function and cellular physiology. Unrestrictive identification of all types of PTMs using mass spectrometry is a powerful approach. Previous efforts have allowed us to successfully develop PTMap v2.0, a tool for genome-wide characterization of protein posttranslational modifications. Initial tests demonstrate that PTMap2 is capable to identify all types of PTMs in E. coli protein database from a single mass spectrometry data file. Here we propose to extend the application of PTMap2 tool to identify unknown PTMs in diverse cellular organisms.